1. Field of the Invention
The tubular expandable cover disclosed herein is in the field of flexible elastomeric or rubber type envelopes used to contain and protect machine parts. These sleeve-like devices are generally known as boots, and are usually tapered and convoluted in form. An important use for such boots is to protect the constant velocity (“C-V”) joints as used in modern automobile drive axles.
2. Prior Art
A typical automobile half axle will carry both an inner and an outer C-V joint each protected by boots. The boots are necessary to retain lubricants and prevent entry of foreign materials. Performance requirements are high, and include longevity, flexibility, limited stretchability, chemical resistance, tolerance to high heat and freezing cold, and the toughness necessary to resist road debris. The outer boot is particularly vulnerable due both to its exposure and the extreme flexing required during steering. Presently there are no sensors available to monitor the condition of the boot and communicate this knowledge to the operator. Unfortunately when the protection of the boot is lost the C-V joint will have a short remaining life.
These requirements have generated a large number of material and conformation studies in an attempt to prevent premature boot failure. Many improvements appear to have come in new materials rather than new structure. In the case of materials, examples of such efforts can be seen in patent application publication 20030137078 to Katoh and U.S. Pat. No. 6,085,797 by Grabaum et al., among many others. For examples of structural changes, U.S. Pat. No. 5,645,286 by Katoh, and U.S. Pat. No. 5,236,394 by Collins et al., can be seen—again among many others. Despite these efforts, boot failure is an ongoing problem due primarily to the inherent fragility of the boot, its harsh usage and exposure to road debris. The material of such boots inevitably degrades with extended use. Therefore it is very probable that boot replacement will be required at some time during the life of most automobiles.
However, boot replacement is difficult because the C-V joint housings at each end of the automotive half-axle are much larger than the interior shaft. It follows that without C-V joint dis-assembly, the shaft sized end of the boot must be passed over the joint housing. This invention allows the boot to expand readily to make this transition, thereby significantly easing the job of boot replacement, particularly when skilled help or special tooling is not available.
While the boot was primarily conceived as a means for ready boot replacement, particularly under field conditions, it will be clear that a boot having this expandable characteristic will also offer significant cost savings to a manufacturer of the drive axles themselves.
Presently, failed C-V boots may be replaced in several ways, one being to remove the entire shaft and replace the boots on the bench. This procedure often requires draining the differential oil, separating a wheel and part of the suspension, then sliding the shaft inner spline through an “O” ring case seal, and finally dis-assembly of at least one C-V joint. Conventional boots may then be installed. However, C-V joints must be disassembled with care, and reassembly is easily botched. If the shaft carries a vibration damper within its reach, additional assembly and reassembly will be required.
The skills and time required for successful fit-up of C-V joints has prompted many technicians to replace the entire axle including shafts, joints and boots as a complete unit. The cost differential to the customer between one needed flexible boot and one complete axle assembly can be readily appreciated.
Therefore it is desirable from the customer's viewpoint to replace the failed boot only. Several methods to reduce the labor and risk incurred by complete removal and axle dis-assembly are in present use. Two methods may be remarked upon, both of which find their best use in replacing the outer boot only, and both of which, unfortunately, compromise boot performance to some degree.
One method uses a type of boot having a lengthwise split or two in its casing. Mating sides of the split carry cooperating elements that locate against each other when the boot is properly assembled around the C-V joint. The split side must be carefully fastened together with screws, rivets, or adhesives according to the particulars of the design. Localized and unusual stress patterns adversely affect the life of such units. U.S. Pat. No. 5,845,911 by Gimino and U.S. Pat. No. 6,139,027 by Biekx address this method. Such a device is offered by J. C. Whitney Co. as part WA556587U.
In another system the smaller shaft end of the boot is stretched radially to pass over the joint housing. A special expanding shoe stretches the shaft end to the housing diameter and holds it there as the boot is forced off the shoe and over the joint housing. The degree of stretch required is formidable. As an example a typical C-V joint may have an input shaft diameter of 30 mm and a housing diameter of 80 mm representing a peripheral increase from 94 to 280 mm. Therefore a significant reduction from the typical boot wall thickness, and choice of a more stretchable material, is often required. An example of a tool for such boot stretching is claimed in patent publication 2004/0261238 by Boudreault. Inner boots cannot be replaced by this stretching method if an intervening vibration damper (which is close to the housing in size) is mounted on the shaft.
With all methods not using a split boot casing, partial dis-assembly of the outer axle support is required to give surrounding access to the C-V joint.